Right from the very beginning, the mass transport of coal, stone and ores was one of the most significant areas of responsibility of railway goods traffic. However, loading and unloading was extremely arduous and time consuming in the early years. Between 1924 and 1926, Deutsche Reichsbahn ordered the serial production of the first self-unloading wagons. The different designs for sand, coal and ore transport varied in length and flap layout. By 1932, DR deployed 520 units of the riveted coal wagons measuring 10 metres in length. The Deutsche Bundesbahn assumed 134 units and gave them the OOTz 23 designation - "z" symbolised its utilisation for ore transport. The "Erz III" lettering was introduced in 1937 and retained by DB. In 1964, 78 OOtz units were still in service.